State the changes in the position, size and nature of the image when the object is brought from infinity up to the concave lens. Illustrate your answer by drawing ray diagrams.

The correct lens formula is :

1. $\dfrac{1}{u} + \dfrac{1}{v} = \dfrac{1}{f}$
2. $\dfrac{1}{u} - \dfrac{1}{v} = \dfrac{1}{f}$
3. f = $\dfrac{uv}{u-v}$
4. f = $\dfrac{u+v}{uv}$

For a convex lens,the value of magnification m is :

1. positive
2. negative
3. both positive as well as negative
4. none

If the magnification produced by a lens is -0.5, the correct statement is:

1. the lens is concave
2. the image is virtual
3. the image is magnified
4. the image is real and diminished formed by a convex lens